[Exodus 9]
{9:1} Then the Lord said to Moses: “Enter to Pharaoh, and say to him: ‘Thus says the Lord God of the Hebrews: Release my people, to sacrifice to me.

God wants to identify Himself from the many Egyptian gods when He tells Moses to refer to Him as "The God of the Hebrews".

{9:2} But if you still refuse, and you retain them,
{9:3} behold, my hand will be over your fields. And a very grievous pestilence will be upon the horses, and the donkeys, and the camels, and the oxen, and the sheep.

Livestock Egyptian gods were Apis (bull god), Hathor (cow goddess).

None of the Egyptian gods could do something against their calamities, but the true one God does deliver His people (Psalm 78 [77]: 48 ).

{9:4} And the Lord will cause a miracle between the possessions of Israel and the possessions of the Egyptians, so that nothing at all will perish from those things which belong to the sons of Israel.”

God makes a distinction between His people (the people who adore the one True God) and the people who are not His (do not adore Him).

{9:5} And the Lord appointed a time, saying: “Tomorrow, the Lord will accomplish this word in the land.”

The appointing of a time is to specify the true miracle, so no one can say that it's just a natural event. Similarly at Fatima, our Lady appointed the time when the miracle of the sun was going to happen for the people to witness it.

{9:6} Therefore, the Lord accomplished this word the next day. And all the animals of the Egyptians died. Yet truly, of the animals of the sons of Israel, nothing at all perished.
{9:7} And Pharaoh sent to see; neither was there anything dead of those things that Israel possessed. And the heart of Pharaoh was hardened, and he did not release the people.

The Pharaoh cared about himself, so as long as nothing happened to him, his loved ones or his personal belongings, he could care less about anyone or anything else.

{9:8} And the Lord said to Moses and to Aaron: “Take handfuls of ashes from the oven, and let Moses sprinkle it into the air, in the sight of Pharaoh.
{9:9} And let there be dust upon all the land of Egypt. For there will be sores and swelling pustules on men and on beasts, throughout the entire land of Egypt.”
{9:10} And they took ashes from the oven, and they stood in the sight of Pharaoh, and Moses sprinkled it in the air. And there came sores with swelling pustules on men and on beasts.

God could have done this through an Angel (as he will do on another event Rev 16:2). All belongs to God (Deut 10:14).

Sekhmet was the goddess of disease control or healing. Could this goddess do something? No.

{9:11} Neither could the sorcerers stand in the sight of Moses, because of the sores that were on them and on all the land of Egypt.

At this point, it is clear that none of the "gods" from Egypt could do something against the power of Almighty God.

{9:12} And the Lord hardened the heart of Pharaoh, and he did not listen to them, just as the Lord said to Moses.

As explained before in previous chapters, the expression "the Lord hardened the heart of Pharaoh" (or similar connotation), does not mean that the God intervened against the Pharaoh's free will. What it means is that the Pharaoh, could not accept the fact that an unknown God to him (a God apart from his Egyptian gods. A God from the people he belittles, the Israelites), could intervene in his life and be more powerful than him. It is due to the pharaoh's arrogance that he did not acceded to Moses' request. All these plagues were actually graces from God to the Pharaoh to let him know that he is not all powerful as he thinks, that he is nothing compared to the true One God. But he refused all these graces. So it is very likely that he was in state of actual mortal sin. God foretold this to Moses because He is beyond time and space so He knew that the Pharaoh was going to continue with a hardened heart out of his own free will.

{9:13} And the Lord said to Moses: “Rise up in the morning, and stand in the sight of Pharaoh, and you will say to him: ‘Thus says the Lord God of the Hebrews: Release my people to sacrifice to me.
{9:14} For at this turn, I will send all my plagues upon your heart, and upon your servants, and upon your people. So may you know that there is no one like me in all the earth.
{9:15} For now, extending my hand, I shall strike you and your people with pestilence, and you will perish from the earth.
{9:16} But it was for this reason that I appointed you, so that I may reveal my strength by you, and so that my name may be described throughout all the earth.

Notice that God uses Moses (a weak human person) to reveal his power. He could have done it Himself if He wanted. As a matter of fact, He doesn't need us at all to do His things. He made the universe. He created it all. But God wants to do things through humans for human important endeavors.

{9:17} Do you still retain my people, and are you still unwilling to release them?
{9:18} So then, tomorrow, at this same hour, I will rain down exceedingly great hail, such as has not been in Egypt from the day that it was founded, even until this present time.

Here our Lord appoints the day and even the hour when the next miracle was going to happen.

{9:19} Therefore, send immediately and gather together your cattle, and all that you have in the field. For men and beasts, and all things that will be found outside, not gathered in from the fields, and on which the hail will fall, shall die.’ ”
{9:20} He who feared the word of the Lord among the servants of Pharaoh caused his servants and cattle to flee together into the houses.
{9:21} But he who neglected the word of the Lord released his servants and cattle into the fields.
{9:22} And the Lord said to Moses: “Extend your hand into the sky, so that there may be hail in the entire land of Egypt, on men, and on beasts, and on every plant of the field in the land of Egypt.”
{9:23} And Moses extended his staff into the sky, and the Lord sent thunder and hail, and also lightning dashing across the earth. And the Lord rained down hail upon the land of Egypt.
{9:24} And the hail and intermingled fire drove on together. And it was of such magnitude as had never before been seen in the entire land of Egypt, from the time when that nation was formed.
{9:25} And the hail struck, throughout all the land of Egypt, everything that was in the fields, from man even to beast. And the hail struck down every plant of the field, and it broke every tree of the region.

Nut was the Egyptian goddess of the sky. Could this goddess do something? Nothing either.

{9:26} Only in the land of Goshen, where the sons of Israel were, did the hail not fall.

The separation of the region of Goshen where the Israelite people were (Gen 47:1) from the falling of thunder and hail, is an indication that the living God does what He says.

{9:27} And Pharaoh sent and called Moses and Aaron, saying to them: “I have sinned even until now. The Lord is just. I and my people are impious.
{9:28} Pray to the Lord, so that the thundering of God and the hail may cease, so that I may release you, and so that you may by no means remain here any longer.”

Here the Pharaoh appears to be cooperating with actual graces but truly not to come back to the state of sanctifying grace because his acts are out of selfish love. This was not an act of selfless love of God and neighbor. He just wanted this event to stop because it was affecting him. So he looks at himself.

{9:29} Moses said: “When I have departed from the city, I will extend my hands to the Lord, and the thunders will cease, and the hail will not be, so that you may know that the earth belongs to the Lord.
{9:30} But I know that both you and your servants do not yet fear the Lord God.”

Moses realizes that the Pharaoh is conceding out of selfish love, not supernatural love (agape).

{9:31} And so, the flax and the barley were damaged, because the barley was growing, and the flax was already developing grains.
{9:32} But the wheat and the spelt were not damaged, because they were late.
{9:33} And Moses, departing from Pharaoh out of the city, reached out his hands toward the Lord. And the thunders and hail ceased, neither did there drop any more rain upon the land.

God listens to Moses, not the Pharaoh.

{9:34} Then Pharaoh, seeing that the rain, and the hail, and the thunders had ceased, added to his sin.

The Pharaoh "added to his sin", so he was already in sin. That apparent act of piety was not out of true selfless love.

{9:35} And his heart was weighed down, along with that of his servants, and it was hardened exceedingly. Neither did he release the sons of Israel, just as the Lord had instructed by the hand of Moses.

When a person is in a state of actual of mortal sin, and when that person adds more mortal sins after another, is very hard for that person to return to the state of grace. He can do so, for he is free and God's graces never ceases to be offered, but if a person is a stiff neck, it is harder.